Permanent magnet assembly



June 11, 1968 w. c. SMITH PERMANENT MAGNET ASSEMBLY Filed June 14, 19655 Sheets-Sheet 1 FIG-3.

INVENTOR William C. Smith BY ATTO NEY June 11, 1968 w c, sMlTH 3,387,707

PERMANENT MAGNET ASSEMBLY June 11, 1968 w. c. SMIII'H 3,387,707

PERMANENT MAGNET ASSEMBLY Filed June 14, 1965 5 Sheets-Sheet 3 3,387,707PERMANENT MAGNET AfisEMllLY William C. Smith, Blairsville, Pa, assignorto Westinghouse Electric Corporation, Pittsburgh, Pa, :1 corporation ofPennsylvania Filed June 14, 1965, Ser. No. 463,706 10 Claims. (Cl.Elf-223) ABSTRACT OF THE DISCLQSURE A magnetic unit having a pair ofpoles at a working face, the polarities thereof conferred by a firstmagnet body, with a pair of magnet bodies remote from the working faceconnected in series by a soft magnetic member and operating in parallelwith said first magnet body.

This invention relates to magnet assemblies particularly useful, by wayof example, in magnetic separators for the resolution of magnetic oresinto a desired mineral fraction and a gangue fraction. It also concernsapparatus that includes such magnet assemblies.

There are a number of commercial models of magnetic separators availableon the market. In these devices, which are of a contacting drumconfiguration, electromagnets or permanent magnets and pole pieces arearranged relative to an outer surface of the drum, designated theseparation surface, to exert a magnetic influence along that surfacewhereby magnetic mineral constituents of ores, for example, areattracted and held there and can thus be separated from the remainingnonmagnetic constituents, commonly designated as gangue. The separationsurface generally is rotated relative to the magnet arrangement in whichmovement the gangue does not participate and falls away, and theseparated magnetic mineral materials are thus removed from the gangueand carried to a place where they can be collected. The presentinvention is particularly directed to magnetic sep arators employingpermanent magnets.

Analysis of the prior art permanent magnet arrangements in these devicesdemonstrates the existence of significant drawbacks by which about /2 toA of the magnetic flux is not utilized. Thus, in many such devices,substantial spaces such as air gaps are located between the permanentmagnets and magnetic flux exists in or passes through those spaces.Since the spaces are within the drum and between adjacent magnets, it isevident that this internal flux constitutes a leakage or a loss of fluxcompared to the total that should be available to I effect magneticseparation. In still other designs, the spaces between magnets have beeneliminated or avoided by placing pole pieces therein and to an extentthis eliminates internal flux between adjacent magnets. However, in sucharrangements, magnetic flux passes between the pole pieces rearwardly ofthe magnets. Hence, while a portion of the magnetic flux extendsexternally of the conveyor surface and is useful, another andsignificant portion appears rearwardly of the magnet and pole assemblyand thus is Wholly removed from any area where it can exert a usefulinfluence for the intended purposes. Such known pole piece arrangement,therefore, simply relocates internal flux leakage and does not eliminateit. Similar problems exist with regard to magnet chucks or assembliesused in conveyors, in sheet spreaders and other applications.

The present invention is an improvement on the device disclosed in thecopending applications Ser. No. 254,223, filed Jan. 28, 1963, now PatentNo. 3,209,912, and Ser. No. 296,041, filed July 18, 1963, now Patent No.3,283,- 900, both assigned to the assignee of the present invention.

United States Patent It is the primary object of the present inventionto provide a novel arrangement of magnets and pole pieces particularlyuseful in magnetic apparatus in which an increased field intensity isobtained with improved utilization of magnetic material in that the fluxdensity in all sections of the magnet assembly closely corresponds tothat of the maximum energy product.

Another object is to provide magnetic separator, conveying and spreadingapparatus including an assembly of permanent magnets and pole piecesproviding for an efficient utilization of the maximum amount of themagnetic flux at the separator surfaces in accordance with the foregoingobject.

Other objects and advantages of the invention will be apparent from thefollowing detailed description and drawings, in which:

FIGURE 1 is a sectional view of a magnetic unit in accordance with thisinvention;

FIG. 2 is another embodiment of a magnetic unit in accordance with thisinvention, a pair of such units is illustrated;

FIG. 3 is a diagrammatic illustration in elevation of a magnetic drumseparator;

FIG. 4 is a perspective view showing a permanent magnet assembly for usein a drum separator, the assembly of magnets being arranged inaccordance with this invention;

FIG. 5 is a cross-sectional view taken along line V--V of FIG. 6; and

FIG. 6 is a cross-sectional view taken along line VIVI of FIG. 5.

Basically, the objects of increased field intensity and improvedmagnetic flux distribution are attained in the present invention by anovel magnet unit including at least three bodies of oriented permanentmagnet material, two of which are arranged magnetically in series witheach other and magnetically in parallel with the third body. As a matterof convenience, the invention will be first described as embodied in asingle magnetic unit, and then as embodied in a magnetic assembly whichincludes a plurality of magnetic units.

The magnetic unit on which this invention is based is a structurecomposed of soft magnetic pole pieces or members, at least three bodiesof permanent magnetic material and a soft magnetic yoke member. Thesethree elements of the magnetic unit are shaped, arranged and assembledto provide at the Working face a first elongated pole face of onepolarity, and a second elongated pole face of the opposite polarityspaced from said first pole face and substantially parallel thereto.

More specifically, the magnetic unit of this invention is characterizedby a yoke of low reluctance material such as iron having angled armspositioned rearwardly away from the working face of the assembly andhaving at least two permanent magnet bodies fitted on the forward sideof each of the arms thereof. In this unit the arms of the yoke provide alow reluctance path of neutral polarity between the magnet bodiesthereby connecting said magnet bodies in series. The pole pieces arearranged at the end of the magnet bodies opposite to the end in contactwith the yoke. An additional permanent magnet body is positioned betweenand in contact with the pole pieces, magnetically in parallel with saidfirst mentioned magnet bodies. For reference purposes, the magnet bodypositioned between the poles may be called the primary magnet body andthe magnet bodies contacting the rear surface of the pole pieces may becalled secondary magnet bodies.

The pole pieces and yoke are held in fixed spaced relation to each otherand to the bodies of the magnetic material which are associated withthem. The bodies of permanent magnet material are positioned so as toconfer one polarity upon one magnetic pole piece and the oppositepolarity upon the other pole piece. Thus, the yoke supports the rearsurfaces of the secondary magnetic bodies abutting it, and a pole pieceabuts the forward surfaces of these magnet bodies and the end surface ofthe primary magnetic body. The magnet bodies are magnetized in adirection that is perpendicular to the planes of the pole surfaces withwhich they are in contact.

The yoke provides supporting structure for the magnetic unit and has atleast two magnet bodies fixed to the forward side of the yoke surfacesextending to the rearward surfaces of the pole piece and to the primarymagnet body which is positioned along the working face of the unit. Theyoke may alternatively be formed of an angle, solid bar of triangular,square, sector or rectangular cross-section of soft iron or steel orother suitable material. It will be understood that the yoke surfacesmay be flat or curved with correspondingly shaped magnet bodiespreferably fitting closely thereagainst.

In utilizing the basic unit described, ordinarily a plurality of unitswill be employed depending upon the number of poles desired. Unitsassembled adjacent each other will share pole members. For example, afive-pole arrangement may be obtained by empolying four of the describedyoke-magnet bodies and pole piece assemblies. In this manner, a magnetassembly is achieved in which a high flux density is attained and theflux density in all sections of the magnet body closely correspond tothat of the maximum energy product. Further the efliciency achievedapproaches 100 percent, based on the better utilization of the magneticflux relative to the working face, for the structural and magneticarrangement of the present invention takes a form in which substantialopen spaces between permanent magnets can be greatly reduced oreliminated and concentrates and conducts the magnetic flux into the areawhere it can be utilized almost entirely to effect a desired object, forexample, a magnetic separation.

In one embodiment, the magnetic unit of this invention takes a form inwhich the yoke is V shaped or angular in cross-section with the arms ofthe V set at a suitable angle with respect to each other and the apex inthe direction of the working face. The pole pieces are bars having, incross-section, a lower surface thereof generally parallel to a surfaceof the proximate arm of said yoke. A pair of secondary magnets, or apair of stacks of slab-shaped magnets, are secured between the adjacentsurfaces of the yoke and the pole pieces and a third magnet or primarystack of magnets is secured between the poles of the unit. The secondarypairs of magnets associated with both arms of the yoke are magneticallyin series and the yoke provides low reluctance coupling therebetween ofneutral polarity. This pair of magnets is magnetically in parallel withthe primary magnet or stack of magnets positioned between the poles.

Referring now to the drawings there is shown in FIG. 1 a magnetic unitin accordance with this invention. This magnetic unit has a pair of polepieces 1, 2 at the working face thereof and a yoke member 3 spaced fromthe pole pieces having surfaces parallel to the rearward surfaces 4, 6of the pole pieces. The yoke member 3 has a generally V configurationwith the apex of the V in the direction of the working face. Between thespaced poles 1, 2 there is positioned a primary stack of magnets 11 to16 abutting a lateral face 7 of one pole piece at one end of said stackand abutting a lateral surface 8 of the other pole piece at the otherextremity of the said stack.

Between the rearward surface 4 of the pole piece 1 and the parallelsurface of the yoke 3 is a secondary stack of magnets 17, 13. A similarstack of magnets 19, 21 is located between the rearward surface 6 of theother pole piece 2 and the parallel surface of the yoke 3. The magneticstacks indicated by the numerals 17, 18 and 19, 21 are magnetically inseries, with the yoke 3 providing a low reluctance magnetically neutralpath for the flux therebetween This pair of magnet stacks ismagnetically in parallel with the primary magnetic stack identified bythe numerals 11 to 16.

in FIG. 2 a very similar magnetic unit 3!) is shown paired with anidentical magnetic unit 50. In this embodiment of the magnetic unit theyoke forms a very shallow V and consequently, the magnetic stack at theworking face 31 to 36 is formed of slabs which are progressively wideras the distance from the poles increases. Thus, in cross-section thisstack of slabs forms a deep V which may touch the apex of the yoke as inFIG. 2 or may be remote therefrom as in FIG. 4. The operation of theunit is essentially identical to that of the embodiment shown in FIG. 1.Such magnetic units will ordinarily not be individually employed, butrather, several such units will be employed simultaneously; the magneticunits and in FIG. 2 are shown in assembled relation and clearly,additional units may be added to form an assembly of desired size. Theappearance of a plurality of magnetic units of the type shown in FIG. 1will differ somewhat from an assembly employing a plurality of magneticunits of the type shown in FIG. 3. Thus, around each pole of the FIG. 1type magnetic assembly, there will be grouped, four magnetic stacks, twoprimary stacks at the working face of the magnet assembly and twosecondary stacks abutting the inclined rearward surfaces of the polepiece. This can be more clearly seen in FIG- URE 4 wherein the twoprimary magnet stacks 51 to 56 and the two secondary magnet stacks 41 to48 are positioned about pole 121. When a plurality of units of the typeshown in FIGURE 2 are assembled, it will be noted (as shown in FIG. 2)that each pole piece will have associated with it only three magneticstacks, two primary stacks at the working face of the magnet assemblyand the third secondary stack of magnets abutting the rearward surfaceof the pole piece. Of course, when a plurality of such units areemployed the units wiil share pole pieces. While the end slabs ofmagnetic material in the primary magnetic stack may be of taperedconfiguration, it is clear that the pole pieces may readily beappropriately shaped so that all magnet slabs have a simple rectangularcross-section.

The invention will be further described in detail with reference to theutilization of magnetic assemblies having magnet units with V-shapedyokes in drum type magnetic separators for resolving magnetic ores.However, it is to be understood that this is for purposes ofillustration and is not to be construed as limiting the invention.

The magnetic separator shown in FIGURE 3 comprises a supporting frame 70on which is mounted the active separator unit indicated generally by thenumeral 72. As will be apparent in the detailed description hereinafter,the separator unit structurally comprises a generally cylindrical drum73 of non-magnetic material (such as stainless steel) surrounding anassembly of magnets and pole pieces located along, but spaced from, aportion of the inside surface 74 (FIGS. 5 and 6) of the cylindrical wall75 of the drum 73. The magnet arrangement is supported independently ofthe drum 73 so that the drum can be rotated while the assembly ofmagnets remain stationary.

Accordingly, the drum '73 is supported on the frame 70 by a shaft '76. Amotor 77 operatively connected to the drum 73 through a sprocket andchain arrangement 7-8 attached to the end walls 79 of the drum 73 isalso supported on frame 79. Shaft 76 suitably supports the drum 73 bymeans of bearings 79a attached to the end walls 79.

Internally of frame 70, there is structure by which feed to be resolvedis directed to the external surface of the cylindrical wall of the drumof the magnetic separator unit, and by which the fractions into whichthe feed is resolved can be separately removed. For this generalpurpose, a conduit 62 leads into an L-shaped chamber 64 at one side ofthe frame 70. The materials in the feed that are non-magnetic and thusnot influenced by the magnet assembly pass downwardly along the L-shapedchamber 64 and are withdrawn through an outlet conduit 65 and are storedor otherwise disposed of as desired. The magnetic materials in the feedare attracted and held to the external surface of the sidewall of thedrum until they are carried beyond a point where they could fall intothe path to the outlet conduit 65. Once they have been carried beyondthis point, they are permitted to drop into a bin or outlet conduit 66provided to receive them.

Within the drum 73 is the permanent magnet assembly, indicated by thenumeral in FIG. 4. The arrangement of the permanent magnets and polepieces in this embodiment of the invention is shown in FIGS. 4 and 5.This apparatus includes a pair of supporting end plates 82 and 84 havingcross bar means 95 and 96, respectively, associated with each by whichthe magnet assemblies can be supported. If desired, adjustable means,such as set screws (not shown) may be provided to lock the end plates 82and 84 in any desired fixed position on shaft 76. The permanent magnetsand pole pieces preferably are maintained as close as possible to theinside surface 74 (FIG. 5) of the drum side wall consistent with thefree rotation of the drum relative to the magnet assembly,

The actual width of each magnet body or stack of magnet slabs preferablyis determined so that available volume between the yoke and the polepieces is substantially entirely filled with magnetic material andvoids, if any, are minimized. However, it will be understood that inmaking the magnet slabs. it is difiicult and expensive to providecomplicated cross-sections, tapered shapes and other special forms. Inmany cases then, magnet slabs of simple rectangular cross-section willbe employed at some loss in efliciency due to the voids resulting frommismatching of slabs. A pole piece having a rear surface there ofabutting a forward surface of a secondary magnet body extends to theworking face of the magnet unit. Successive poles define a space inwhich is positioned a primary magnet body or stack of magnet slabsextending along the working face.

The magnet units as described may be made individually and thenassembled with conventional means used to secure several magnet unitstogether to form a magnet assembly. However, in devices employing aplurality of magnet units, it is convenient and desirable to constructthe device so that adjacent magnet units share pole pieces and means forsecuring the elements of the structure together.

In FIGS. 4 and 5, there is shown a five pole magnet strip assembly 80,which includes a plurality of magnet units sharing pole pieces andsecured together and afiixed to the end plates 82 and 84 of the magneticseparator. The device shown is provided with four magnet units 101, 102,103, 104 each having a yoke 110, 111, 112 and 113. The two middle magnetunits 102, 103 share three appropriately shaped pole pieces 121, 122 and123 while the end magnet units 101, 104 each have one pole piece 120 and124, respectively, which is not shared. The magnetic strip is heldtogether in part by a pluralityof threaded means 85 located betweenadjacent magnet units which are threaded at one end into the pole pieces121, 122, 123 and atthe other end are provided with collars 81 whichextend into abutting relation with the rearward edge of adjacent arms ofthe yokes 110, 111, 112, 113. It will be noted that by tightening thenut 83, the magnet stacks of adjacent magnet units can be drawn firmlyto their respective yokes. The support of the flank magnet stacks of theend magnet units 101 and 104 requires that a hole 86 be drilled in onearm of the yoke and the magnet stack so that the fastening means 35, 83may effectively draw the pole piece 120, for example, and the magnetstack to the yoke. The magnet slabs in the primary magnet stack may beglued with epoxy cement to each other and to the pole pieces or othersuitable means may be employed.

To secure the magnet units to the end plates 82 and 84, the horizontalcross bars 95 and 96, respectively, are welded or otherwise securedthereto. The cross bar 95 is provided with downwardly extending struts91 and 92, and the cross bar 96 is similarly provided with struts 93 and94. The struts are welded or otherwise secured to the cross bars. Aswill be seen in FIGS. 4 and 5, the ends of the cross bars 95 and 96closely fit into the angle formed by the rear surfaces of the end yokes11-0 and 113. The cross bars are preferably welded to the yokes.Downwardly extending struts 91 and 93 closely fit into the angle formedby the rear surfaces of the yoke 111. Similarly, the struts 92 and 94mate with the rear surfaces of yoke 112. The struts are preferablywelded to the yokes. It is clear that an extremely strong structure hasthus been provided.

In the embodiment shown in FIG. 4, there are four magnet units that, inthe aggregate and in view of their arrangement, contribute five poles.Additional magnet units each contribute one more pole, and accordingly,any odd or even number of poles desired can be easily provided. Where a360 arc of magnet units is employed, an even number of poles isobtained, for the final magnet unit merely closes and contributes noseparate pole. While the magnetic assembly of the invention has beendescribed primarily in terms of a V configuration, in which the yokearms are fixed at about a angle to each other, other angles, smaller orgreater, may be used.

For a drum type magnetic separator of the type being discussed, adiameter of 30 to 36 inches frequently is used and the drum may be asmuch as 4 to 6 feet in length. The individual permanent magnets usedwould be functionally of substantially similar length, though thatlength can be achieved by using a plurality of magnets each of a smallerlength so that in the aggregate the 4 to 6 feet of magnets is attained.Of course, the pole pieces also extend the full length, and similarly,the full length required may be achieved by using a plurality of smallerpole pieces in contact with each other.

The materials used to produce the permanent magnets and pole pieces inaccordance with this invention can vary widely, as is apparaent to thoseskilled in the art. Preferably, they are made from ceramic permanentmagnet high coercive force materials such as the barium ferrites, orstrontium ferrites or other materials of like character, since thearrangement provides a large magnet area in relation to the magnetlength. However, the metallic permanent magnet materials such as alnico,and the like can be used. Similarly, the pole pieces can be made of anysoft magnetic material desired. Particularly suitable are iron andcommon soft steel.

While the invention has been described primarily as employing orientedmagnetic material, and indeed this is the preferred material, it is alsocontemplated that isotropic high coercive force permanent magneticmaterial may be used in the magnetic assembiles of the invention. Inusing such material, the arrangement is such that directions of strongmagnetization of the permanent magnetic material essentially impart onepolarity thereof to one of the pole pieces of the magnet assembly, andthe other polarity to the other pole piece.

As has already been indicated, the pairs of magnets, or pairs of stacksof magnets in contact with the yoke are magnetically coupled in series.Consequently, if the south pole of one magnet (or stack) is adjacent onepole piece, the north pole of the same magnet is adjacent the yoke,while for the companion magnet (or stack) of the same magnet assembly,the south pole is adjacent the yoke and the north pole is adjacent theother pole piece. These two magnets or stacks of magnets of each magnetassembly are magnetically in series due to their opposite magneticorientation and to the presence of the yoke which provides a neutralpolarity low reluctance path between the stacks. The stack of magnets atthe working face etween the lateral surface of the pole pieces ismagnetically in parallel with the paired stacks and cooperates with themto increase the flux at each pole.

In consequence of the just described arrangement of pole pieces andmagnets, internal flux leakage is minimal because it occurs only at theends of the magnet assemblies, along one side of each flank magnetassembly, and at bolt locations and mismatched magnet joints. Moreover,there is little flux leakage rearwardly of the magnet arrangement sincethe flux behind the magnets is concentrated in the yokes and isconducted by the yokes from one of the paired magnets (or stacks) to theother. Hence, the flux is principally located in front of the magnets inan are between the pole pieces and thus substantially all of it, forpractical purposes, is available to effect the desired separation.

Operation of a magnetic separator as just described follows that ofprior art devices. Thus, where an ore is being separated from a gangue,the ore that is to be resolved is comminuted to a relatively small size,for example, from fines ranging up to particles of A to /2 inch or more.For Wet operation, the finely divided ore, is dispersed in a carrierfluid, normally water, and fed to the separator through the inletconduit. With the conveyor or drum surface rotating, the feed passesinto contact with it and the magnetic material is attracted to and heldon the drum surface. The remaining materials pass to the first outletconduit. The drum surface and its magnet assembly are of such size thatthe magnetic force is maintained on the particles on the surface untilthey are carried beyond the area in which they would pass outwardly withthe tailings. Once they are beyond that point, the end of the magneticseparator arrangement is reached and the particles fall away from thedrum surface under the influence of gravity and the failure, due toremoteness of sufiicient magnetic force to retain them. The fallingmagnetic particles are directed to a separate outlet conduit providedfor them. The alternate polarities of the magnetic poles to which theparticles are subjected as the drum surface passes relative to themagnetic drum arrangement, tends to vibrate these particles on thesurface, reorientating them and permitting entrapped nonmagneticmaterial to fall away.

In the resolution of materials with a separator as in this invention bywhat can be termed :a dry process, the feed usually is arranged to passover the rotating surface under the influence of gravity. Normallly fordry separations, more magnetic units are used, often covering on theorder of 50 percent or more of the surface of the separating drum. Insuch practice, the feed may be introduced into contact with theseparating drum near its top and the feed inlet, commonly a simplefunnel arrangement to which a vibrator may be attached if necessary ordesirable, is supported from the frame above the drum. The tailings fallfree of the drum at its side to an outlet provided for them, while themagnetic particles are held to the surface beyond that point and areseparately removed.

Another arrangement, especially suited to dry separations or conveyingapplications, utilize a drum having magnet assemblies along the entireinner surface of the sidewall of the drum. In such instance, the drumsidewall, which is driven, may provide all or part of the motive powerfor the conveyor.

Magnet units or assemblies as described are useful for many otherindustrial applications. For example, they can be used in conjunctionwith conveyors by which cans may be held to a conveyor and moved asdesired. Further, they are useful as spreaders of metal sheets arrangedin stacks.

From the foregoing discussion and description, it is apparent that thepresent invention is a significant advance in magnet units. It will beevident that sizes, number of elements and the like can be changed.Furthermore, the face of the magnet assembly can be made fiat or evenconcave, rather than convex as shown, for particular applications. Tipscan be added to the pole pieces to aid in directing the flux as desired.In all events, the materials of construction for different parts ofapparatus with which the magnet assembly is used should be chosen suchthat no materially adverse influence on the utilization of essentiallyall the available flux exists.

Having illustrated and described the invention in detail for purposes ofexemplification, it should be understood that the invention may bepracticed otherwise and is not to be limited by the details expressed.

I claim as my invention:

1. A magnetic unit having a pair of spaced pole pieces at a workingface, each pole piece having a front surface at the working face and arear surface remote therefrom, a primary permanent magnet bodypositioned at the working face between and in contact with the polepieces conferring one polarity on one pole piece and the oppositepolarity on the other pole piece, a pair of secondary permanent magnetbodies having their polarities magnetically coupled in series through acontacting yoke member of low reluctance material, each member of thesaid pair of secondary magnet bodies contacting one of said rearsurfaces and the primary magnet body, the primary magnet body beingmagnetically in parallel with the secondary magnet bodies.

2. In a magnet assembly comprising a series of pole pieces spaced alonga working face with lateral stacks of slabs of ceramic permanent magnetmaterial filling the space between successive pole pieces, each polepiece having a front surface at the working face and a rear surfaceremote therefrom, the improvement comprising, rearward stacks of slabsof ceramic permanent magnet material contacting said rear surfaces andextending into contact with said lateral stack to increase the magneticstrength at each pole, a yoke of low reluctance material contacting therear surface of each of said rearward stacks of slabs connecting themmagnetically in series by providing an easy flux path of neutralpolarity therebetween and furnishing structural support to the magnetassembly, and the lateral stacks of magnet slabs being magneticallycoupled in parallel with said rearward stacks.

3. A magnet assembly comprising a plurality of parallel elongated polepieces defining a working face, each pole piece having a front surfaceat the working face, a rear surface remote therefrom and a pair oflateral surfaces joining the front surface to the rear surface, primaryoriented permanent magnet bodies contacting the lateral surfaces of saidpole pieces and occupying the space between adjacent pole pieces to theworking face, secondary oriented permanent magnet bodies contacting therear surfaces of said pole pieces and the primary magnet bodies, theseveral oriented magnet bodies about each pole piece conferring aselected polarity thereon with adjacent pole pieces having oppositepolarity, a yoke member of low reluctance material contacting the rearsurfaces of the secondary magnet bodies connecting them magnetically inseries and providing structural support to the magnet assembly, and theprimary magnet bodies magnetically coupled in parallel with theirassociated secondary magnet bodies.

4. A magnet assembly comprising a series of spaced elongated pole piecesdefining a working face, the pole pieces lying generally in parallelalignment, each pole piece having a front surface in the plane of theworking face and a pair of elongated spaced lateral surfaces extendingrearwardly therefrom to join at least one rear- Ward surface, primarybodies of oriented permanent magnet material positioned between and incontact with the lateral surfaces of successive pole pieces therebyfilling the space between pole pieces to the working face, secondarybodies of oriented permanent magnet material positioned in contact withthe rearward surfaces of said pole pieces and said primary magnetbodies, each pole piece thus being in contact with at least two orientedmagnet bodies which cooperate to confer a desired polarity thereupon sothat each pole piece has a polarity which is opposite to that of itsnearest neighboring pole piece, a yoke member of low reluctance materialpositioned in contact with the rearward surfaces of said secondarymagnet bodies connecting them magnetically in series by providing aneasy flux path of neutral polarity therebetween and capable of affordingstructural support to the magnet assembly, each primary magnetic bodybeing magnetically coupled in parallel with at least two secondarymagnetic bodies.

5. An assembly of magnets for use in separating proce dures andconveying applications comprising a pair of elongated magnetic polepieces of opposite polarity defining between them the working face ofsaid magnet assembly, an elongated yoke member of low reluctancematerial having a pair of convergent inclined surfaces extending thelength thereof, the convergence of said surfaces forming an apex in thedirection of said working face, each of said elongated pole pieces lyingparallel to and spaced from one of said inclined surfaces, a primarybody of oriented permanent magnet material disposed along the workingface of said magnet assembly having a direction of magnetizationessentially parallel to said working face and substantially filling thespace between said pole pieces, a pair of bodies of oriented permanentmagnet material each substantially filling the space between one of saidinclined surfaces and the pole piece associated therewith and extendingto said primary body of oriented permanent magnet material, said pair ofbodies of oriented permanent magnet material being arranged with theirpolarities magnetically coupled in series through the yoke member andthe polarities of said pair being magnetically coupled in parallel withsaid primary body.

6. The magnetic assembly of claim wherein the angle between theconvergent surfaces is approximately 90.

7. An assembly of magnets for use in separation procedures having aworking face thereon comprising a generally elongated yoke of lowreluctance material including a pair of convergent inclined surfacesextending the length thereof, the convergence of said inclined surfacesforming an apex in the direction of the working face of said assembly, apair of elongated magnetic pole pieces spaced along the working face ofthe assembly, said pole pieces extending parallel to said yoke andsymmetrically spaced therefrom, each of said pole pieces having aninclined surface substantially parallel to one of the inclined surfacesof the yoke with which it cooperates, a primary stack of orientedpermanent magnets disposed along said working face having its directionof magnetization essentially parallel to said working face and extendingbetween and into contact with cooperating surfaces of said pole pieces,a secondary stack of oriented permanent magnets positioned between andcontacting one of said inclined surfaces of said yoke and the parallelinclined surf-ace of the cooperating pole piece, another secondary stackof oriented permanent magnets positioned between and contacting theother of said inclined surfaces of said yoke and the parallel inclinedsurface of the pole piece with which it cooperates,

the sevenal stacks of oriented permanent magnets substantially fillingthe volume between the inclined surfaces of the yoke and the pole piecesand the working face of the assembly, the oriented permanent magnets ofthe secondary stacks being arranged with their polarities magneticallycoupled in series through the yoke, and the oriented permanent magnet ofthe primary stack being arranged with its magnetic polarity magneticallyin parallel to that of the secondary stacks.

8. The magnetic assembly of claim 7 wherein the angle between theconvergent surfaces is approximately and the magnets are composed of aferrite material.

9. In a magnetic separator, a drum having a cylindrical sidewallcomposed of a non-magnetic material and mounted for rotation on a shaft,a permanent magnet unit having two poles at a working face thereofadapted to attract magnetic material to be separated toward the externalsurface of the sidewall of the drum and mounted within the drum, saidWorking face being positioned in close proximity to the internal surfaceof said sidewall, the magnetic unit comprising a V-shaped yoke of lowreluctance soft magnetic material having two arms extending away fromthe working face thereof, .a pair of pole members of low reluctance softmagnetic material each spaced from and parallel to an arm of said yoke,bodies of oriented permanent magnetic material substantially completelyfilling the spaces between the arms of the yoke and the pole pieces andextending to the working face of the magnetic unit and comprising aprimary body of oriented permanent magnet material disposed along saidworking face with its direction of magnetization essentially parallel tosaid working face and extending between and into contact withcooperating surfaces of said pole.

pieces and conferring one polarity on one pole piece and the oppositepolarity on the other pole piece, a secondary body of oriented permanentmagnet material disposed between and contacting one of the arms of theyoke and one of said pole pieces, and another secondary body of orientedpermanent magnet material disposed between and contacting the other armof the yoke and the other of said pole pieces, the secondary bodies oforiented permanent magnet material being magnetically coupled in seriesthrough said yoke and being magnetically in parallel with said primarybody.

10. In a magnetic separator in accordance with claim 9, at least twosuch permanent magnet units adjacent one another and sharing a commonpole, the oriented permanent magnet bodies consisting of stacked ceramicpermanent magnets in slab form.

References Cited UNITED STATES PATENTS 2,146,588 2/1939 Merrill 2092l92,992,737 7/1961 Buus 209223 3,067,366 12/1962 Hofman 335306 3,168,6862/1965 King 335306 3,209,912 10/1965 Sloan 209--223 3,283,900 11/1966Sloan 209-223 2,992,736 7/1961 Buus et a1. 2,992,738 7/ 1961 Maynard.

HARRY B. THORNTON, Primary Examiner.

R. HALPER, Assistant Examiner.

